Thursday, October 31, 2013

In our last post, we looked at some members of the M16 family. We also mentioned that the M16A2 model is a very influential model in the M16 family and is still in use in various military forces. We will continue to look at other members of the M16 family in this post.

M16A4: This rifle is the fourth generation rifle in the M16 series. One of the main differences between this model and the models we've have already studied so far is that the carrying handle on this model is detachable. What the designers did was put picatinny rails on the rifle and also on the hand guards. The carrying handle is attached to the picatinny rail on top and can be removed and replaced with other accessories, such as a reflex sight, night vision device etc. In addition, other accessories may also be attached to the other rail mounts, such as a laser, vertical grip, flash light etc.

The M16A4 rifle. Click on image to enlarge. Public Domain Image.

In the above image, note that the carrying handle has been replaced by a telescopic sight called an ACOG (Advanced Combat Optical Gunsight) and the rifle has an additional vertical grip attached to the hand guard in front. The M16A4 has the same firing modes as the M16A2 (i.e. single shot and 3 round burst) and also retains a bunch of other features from it.

The US Marines were the first to adopt this rifle model and are in the process of phasing out their existing M16A2 rifles with the M16A4. It is also used by some other countries' military forces around the world, such as Thailand, Turkey etc.

M4 Carbine: During the Vietnam war, Colt developed a carbine version of the M16A1, called the CAR-15. Around 1988, there came a need for another carbine design and Colt based it off the influential M16A2 design. The M4 carbine features a shorter 14.5 inch barrel and a telescoping stock. Therefore, it is more compact than the M16A2. It also borrows from the M16A4, by incorporating the rails and the detachable carrying handle, therefore allowing it to accept a wide variety of accessories.

US Soldier carrying a M4 with accessories attached. Click on image to enlarge. Public domain image

Due to its shortened barrel, the ballistic performance of the bullets is slightly worse than the M16A2. However, the smaller length makes it more suitable for close quarter battle. The M4 carbine was first selected for use in 1994, by the US Army, initially to replace the M9 pistol and the M3/M3A1 submachine gun. Later on, they began to replace the M16A2 rifles as well and the US Marines also adopted it for use by officers. Other branches of the military started using it as well and it is also used by other countries around the world.

One variant of the M4 is the M4A1 carbine, which is used by US Special Operations units, such as the Navy SEALs, Army Special Forces, Marines Force Recon, USAF Para-rescue etc. The difference is that while the M4 is capable of single shot and three round burst firing modes, the M4A1 is capable of single shot and fully automatic firing modes.

AR-15: The original prototype of the first M16 model was called the AR-15 (after the company Armalite, which was the original designer of this rifle family). However, after Colt bought the design, they called their model the M16 and made a civilian model of the design in 1963, which they named the AR-15. In this discussion, we will only talk about the civilian models released by Colt and other manufacturers, as few examples of the original Armalite design exist. The AR-15 was designed for civilian sales and while it does have a resemblance to other members of the M16 family, there are some very significant differences. The first major difference is that the AR-15 only has one firing mode (semiautomatic mode, which means you have to pull the trigger each time to shoot a new cartridge). Therefore, it is NOT an assault rifle, since it is incapable of switching firing modes. While the external appearance of an AR-15 is almost identical to a fully automatic M16 family model, the internals are very different. The hammer and trigger are of a different design and the bolt carrier and lower receiver are differently shaped that they cannot be interchanged with a M16 mechanism. This is done to satisfy United States firearm laws that semi-automatic weapons cannot be easily converted to fully-automatic weapons.

Colt AR-15 A3 Carbine Model. Click on image to enlarge.

There are multiple models of AR-15, resembling various other variants of the M16 family. While Colt officially holds the trademark to the term "AR-15", clones are made by many other manufacturers and they are unofficially all referred to as "AR-15". Many of these clones are designed to fire other calibers of ammunition, ranging from small pistol cartridges, to many different rifle calibers and even shotgun shells.

These are only some of the popular variants of the M16 family. There are other international variants that we will study in our next post.

M16: This is the first operational version of the rifle and was only adopted by the US Air Force initially. Among its distinctive features are a triangular shaped forward hand guard, no cleaning compartment in the stock (as Colt famously declared that this rifle was so advanced that it didn't need one), no forward assist lever and a duckbill shaped flash suppressor at the muzzle. The original version was issued with a 20 round magazine. It is capable of selecting firing modes and can fire in single-shot as well as fully automatic modes. The barrel has a rifling twist of 1 turn in 12 inches.

Original M16 rifle. Click on image to enlarge. Public domain image.

In the above image, we see an original M16 rifle. This variant was adopted by the US Air Force, which continued to use this model until 2001 before switching to the M16A2 variant. It was also used by some other military forces, notably the British SAS.

M16A1: This is the variant that was first accepted by the US Army. Soon after the original M16 was ordered by the US Air Force, the Army got in the act and asked for a model with a few changes to it, notably, the addition of a forward assist lever, in case the cartridge did not properly seat in the chamber. Colt and the US Air Force believed that this change was unnecessary, over-complicated the weapon and increased its cost by $4.50. Hence, the Air Force got the M16 variant and the Army got the M16A1 variant., which has the forward assist lever. One more difference is that the duckbill flash suppressor was found to pick up twigs and leaves in jungle conditions and was replaced by a bird-cage style flash suppressor. This variant retains the same triangular forward hand guards, selectable firing modes (single-shot and fully automatic) and rifling twist of the original M16.

The M16A1 rifle. Note the bird-cage flash hider in front of the muzzle and the presence of a forward assist lever.

Early versions of the M16A1 were issued with no cleaning kits and without a chrome lined chamber. This led to a number of jamming issues early on and investigations were made to determine why this was happening. A change in the ammunition formula was found to be the cause, as the new ammunition left more residue in the rifle. Since the rifle was issued without a cleaning kit, soldiers could not properly maintain their weapons and this led to jamming problems in the field. Immediately after the cause was determined, the rifle was changed to include a cleaning kit, stored in a compartment in the stock. The barrel. bolt and chamber were also chromed to resist corrosion. In 1970, the magazine was changed from 20 round capacity to a 30 round capacity, as can be seen in the image above.

After its initial reliability problems were solved, the M16A1 variant became adopted by the US Army and the Marines, as well as other military forces around the world, such as Argentina, Australia, Thailand etc. It is still used by some military forces.

M16A2: This is a very influential version of the M16 family and has a number of differences from the M16A1. Most of the changes were added because of the US Marines. The Marines found that in the Vietnam war, many inexperienced men would put the rifle into fully automatic mode and end up emptying their magazines into the bushes without hitting a single enemy. Hence, they asked for the automatic firing mode to be removed and a three-round burst mode to be added instead. This makes the M16A2 variant capable of firing in single-shot and three round bursts only. Also, NATO forces wanted to use a more powerful version of the 5.56x45 mm. cartridge (the SS109 cartridge). However, the newer cartridge needed the rifling twist of the barrel to be changed, in order to maintain bullet stability in the air. Hence, the M16A2 features a barrel with a twist rate of 1 turn in 7 inches (compared to 1 turn in 12 inches for the earlier models) to work with NATO standard cartridges. The barrel thickness was also increased as the US Marines wanted a stronger barrel to resist bending in the field and not overheat as quickly.

The M16A2 rifle. Click on image to enlarge. Public domain image.

There are also many other major changes. For instance, the material of the buttstock plastic is different and 10 times stronger than the original. The shape of the forward hand guards is round instead of triangular and the two handguard pieces are symmetrical (meaning that either half can fit as the left or right side hand guard). This enables the rifle to be held more easily by smaller hands and the symmetrical hand guards make production easier, as there is no longer a need to manufacture separate left-side and right-side hand guards. The shape of the pistol grip is also different - this version has a notch added to support the middle finger and it has more texture to enhance the grip. Because this rifle is designed to fire the NATO SS109 cartridge, the rear sights are also changed to match this new cartridge's ballistics. Also, the flash suppressor is modified and closed at the bottom, so that it will not kick up dust or snow when fired from the prone position.

This variant was initially adopted by the US Marines and then by the US Army, followed by the other branches of the US military and other military forces around the world. It is still being used by many military forces around the world.

M16A3: This is a variant of the M16A2 model that came out at around the same time as the M16A2. It was produced in small quantities and designed for US Navy SEALS and the Seabee units. The main difference is that while the M16A2 can only fire in single-shot and three-round bursts, the M16A3 can fire in single-shot and fully automatic modes. Special forces are trained to not waste ammunition and hence, this variant allows fully automatic fire.

Thursday, October 17, 2013

Fanning a revolver is a technique often used by trick shooters to increase the rate of fire of single action revolvers. In a single action revolver model (such as the legendary Colt Single Action Army revolver), pulling the hammer back by hand cocks the revolver and also turns the cylinder to the next chamber. Pulling the trigger releases the hammer. Therefore, to fire the revolver multiple times, the user must pull the hammer back first, then pull the trigger to fire it, then pull the hammer back again, pull the trigger again and so on, until the revolver is empty. However, it is also possible to hold the trigger down with one hand and then pull back on the hammer with the other hand and release it and keep doing this rapidly. Each time the hammer is released, it falls and detonates the cartridge in the chamber and each time it is pulled back, the hammer cocks and the cylinder rotates to the next chamber. Since the trigger is held down, the hammer cocks but does not lock back and falls back immediately after it is released. Therefore, the rate of fire is down to as fast as the user can pull the hammer back. In order to do this rapidly, the user usually uses a fanning motion with the cocking hand.

The video above demonstrates this technique. Due to the rates of fire that can be achieved by this technique, it is used by trick shooters and fast-draw competitors.

However, it must be noted that this technique may also damage a revolver's stop mechanism, especially when done very rapidly. One more point to be noted is that it isn't very good for shooting accuracy. There are only a few people that can shoot reasonably accurately with this method. That is one more reason why it is seen in trick shooting shows and not used very much by ordinary people.

Thanks to Hollywood movies, some people are under the impression that this was a standard technique used by cowboys in the 1850s. For an example, here's a scene from the classic western movie "Shane".

The technique of fanning a revolver was definitely known during that era, but the reality is that most real gunfighters did not use this technique in real fights, because of concerns of accuracy. What did real gunfighters think of this technique then? The following quotes are by one of the most famous gunfighters, Mr. Wyatt Earp, taken from an interview he gave later in life:

"In all my life as a frontier peace officer, I did not know of a really proficient gunfighter who had anything but contempt for the gun-fanner, or the man who literally shot from the hip"

"From personal experience and from numerous six-gun battles which I witnessed, I can only support the opinion advanced by the men who gave me my most valuable instruction in fast and accurate shooting, which was that the gun-fanner and the hip-shooter stood small chance to live against a a man who, as old Jack Gallagher always put it, took his time and pulled the trigger once."
"A skilled gun-fanner could fire five shots from a forty-five so rapidly that the individual reports were indistinguishable, but what could happen to him in a gunfight was pretty close to murder."

"Hickok (“Wild Bill” Hickok) knew all the fancy tricks and was as good as the best at that sort of gunplay, but when he had serious business in hand, a man to get, the acid test of marksmanship, I doubt if he employed them. At least, he told me that he did not. I have seen him in action and I never saw him fan a gun, shoot from the hip, or try to fire two pistols simultaneously. Neither have I ever heard a reliable old-timer tell of any trick-shooting employed by Hickok when fast, straight-shooting meant life or death."

These quotes and others are found in an authorized biography, "Wyatt Earp: Frontier Marshall" by Stuart N. Lake, where he gave a personal interview to the author about his life experiences.

Monday, October 14, 2013

After all that stuff we read about headspacing, in the last couple of posts, let's look at a tangential topic here. In the image below, we have three kinds of cartridges, all of .22 caliber, but of different lengths:

From left to right, .22 CB, .22 Short and .22 Long Rifle (LR) cartridges.

Public domain image.

The three cartridges in question are (from left to right), .22 CB, .22 Short and .22 Long Rifle (popularly known as .22 LR). Now imagine that you have a firearm that is designed to shoot .22 LR. Will it be able to shoot the other cartridges?

To answer this question, we must first note that these are rimmed cartridges, i.e. the rims of the cartridges are wider than the body of the cartridges. Also note that although the overall lengths of the cartridges are different, the diameter of the cartridge cases and bullets are identical. Also, the sizes of the rims in all three cases are identical.

That's right, for rimmed cartridges, the headspace is measured as the width of the rim. Therefore, a firearm that can fit a .22 LR cartridge (the longest of the three) can also comfortably fit a .22 short, a .22 Long and a .22 CB. Since all these cartridges have the same rim diameter and rim width, they also headspace correctly. This means that a .22 LR firearm can fire these without the fear of case separation occurring.

Of course, a few caveats must be noted here. The first is that of the .22 Short, .22 Long and .22 LR, they were all originally designed to use the same propellant, black powder, with the .22 LR having the most quantity in the cartridge (the .22 CB is even more low powered than these three). Therefore, a firearm designed for .22 LR is strong enough to handle the pressures generated by the other cartridges. Also, since the .22 LR is the longest of the four cartridges, the other three can fit in the chamber. Since all four of these are rimfire cartridges, the same firing mechanism can be used for all of them. However, it must be noted that just because a firearm designed for .22 LR can be fired with any of these 4 cartridges does not mean it can function after that. For instance, cartridges may have to be manually fed in one at a time, because a .22 LR magazine may not feed the other cartridges properly due to the different lengths of the cartridges. Also, the recoil forces generated by the smaller cartridges may not be enough to cycle the action of a firearm designed for .22 LR properly. Therefore, depending on the type of firearm and its action, the user may have to manually extract and feed smaller cartridges. The sights will also have to be adjusted, since the smaller cartridges have less power and shoot at lower velocities. Hence, while it is possible to safely fire .22 CB, .22 Short, .22 Long and .22 LR out of a firearm designed for .22 LR, there are many reasons why people do not always do so.

One more major caveat -- there are other so-called cartridges in .22 caliber, for instance, the .22 Magnum (a.k.a. .22 WMR or .22 Winchester Magnum Rifle). This cartridge cannot and should not be fired from a rifle designed for .22 LR. For one thing, the two cartridges are actually of different diameters and lengths. On top of that, .22 WMR uses much stronger propellant that .22 LR and therefore generates higher pressures (which is the reason why they increased the diameter and length of the .22 WMR cartridge, so it cannot fit into a .22 LR firearm chamber, otherwise it could be a dangerous situation because the .22 LR firearm may not be able to handle the higher pressure). A .22 LR cartridge can fit in the chamber of a firearm designed for .22 WMR, but since the cartridge is of smaller diameter, when the cartridge is fired, it may split in the chamber and stick to it.

Sunday, October 13, 2013

In our last post, we looked into the subject of "headspacing", we will continue to study our subject in this post. As was suggested in our last post, headspace is the distance between the bolt face and a point in the chamber that prevents further forward movement of a cartridge. Depending on the firearm and the shape of the cartridge, this distance can be different for different types, as the figure below shows:

Click on image to enlarge.

Image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported by user Amendola90 at wikipedia.org

Now we will look into what happens if the headspacing is not correct. There are two scenarios we must consider here. The first is excessive headspacing, where there is extra space between the bolt face and the cartridge in the chamber. The second is insufficient headspacing, where there is too little space between the bolt and the cartridge.

What if there is excessive headspacing? In this scenario, when the firing pin hits the cartridge, it will move forward into the chamber before detonating. When the propellant explodes, the walls of the cartridge will expand due to heat and firmly stick to the walls of the chamber, preventing rearward motion of the cartridge. However, the thicker base of the cartridge will move backwards, because there is now a gap between it and the bolt face and this will cause the walls of the cartridge to stretch. If the stretching is too much, the walls of the cartridge could rupture and release hot gases into the action and also potentially spray case fragments out from the action of the firearm, which could be hazardous to the shooter or people standing next to him.

Well, what if there is insufficient headspacing in the chamber? In this scenario, the back of the cartridge will stick out of it and the user will not be able to close the bolt fully on the loaded cartridge. The user will not be able to properly operate the firearm if this happens. If the user were to force the bolt to close on the cartridge, this pushes the bullet tightly into the case neck and if the firearm is fired, this will cause excessive pressure to build up inside it, leading to hot gases coming out of the cartridge's primer pocket with similar results as excessive spacing. In worst case scenarios, the excess pressure could cause the action to rupture and cause damage to the gun and its user.

So, how do we determine that a firearm has proper headspacing? We can do that by using a set of gauges, called headspacing gauges. These are measuring instruments that are precisely machined to the SAAMI or CIP or military standards of a cartridge caliber. Typically, these are made of heat-treated steel and are machined to tolerances below 0.001 inches or so. They are made for various calibers by several reputable commercial companies at fairly reasonable prices. Typically, there is a "Go" gauge, a "No-go" gauge and (for military specification rifles), a "Field" gauge.

Headspacing gauges. Top is a "No-go" gauge and bottom is a "Go" gauge

The "Go" Gauge: A firearm must be able to close the bolt with no resistance at all, when a "Go" gauge is inserted into the chamber. This signifies that the firearm is able to meet the minimum length specification for the cartridge. If the bolt does not close on the "Go" gauge, this means that the firearm has insufficient headspacing and may be dangerous to fire, even if the user manages to force standard cartridges to fit in the chamber. Sometimes, the cause of this may be a dirty chamber or bolt face, because the accumulated dirt may be thick enough to prevent the bolt from closing on the gauge. However, if the firearm is clean and the bolt still does not close on the "Go" gauge, it must be taken to a competent gunsmith for adjustments.

If a firearm successfully closes on a "Go" gauge, it means that the firearm at least has sufficient headspace, but it may still have excessive headspace. That can be determined with our next gauge.

The "No-go" Gauge: A new (or overhauled) firearm must not be able to close on a "No-go" gauge. If the bolt closes successfully on a "No-go" gauge, this means the firearm has excessive headspace and there is a risk of cartridge cases rupturing inside the chamber. If the firearm is new or recently repaired, that means it should be returned to the manufacturer immediately.

A used firearm may be able to close on a "No-go" gauge, due to wear of the bolt and chamber surfaces, but this means that it should probably go to a gunsmith for repair soon and it may be possible to fire new factory ammunition in it until then, but reloaded ammunition is probably a bad idea and the firearm may malfunction on slightly out-of-spec cartridges. Here's where the test with the third gauge comes in (especially for firearms built to military specifications).

The "Field" Gauge: The bolt of any firearm, whether old or new, should not be able to close on a "Field" gauge. A bolt that closes on "no-go", but not on a "field" gauge, may be considered close to being unsafe, but may work on new cartridges (and should be sent to a gunsmith soon for possible re-headspacing). However, if the bolt closes on a "field" gauge as well, then it is definitely not safe to fire and should be sent for repairs immediately (or mounted on a wall as a decorative piece!).

Some calibers have a fourth gauge called a "Field II" gauge, for which the bolt should never lock on. This type of gauge is only used by some rifles (for example, Colt uses it to reject M-16 rifles).

It must be noted that gauges are usually manufactured to either SAAMI, CIP or military standards and therefore may have different dimensions, even for the same caliber cartridge. Therefore, it may be possible that a rifle manufactured to NATO specifications, may lock on a "No-go" gauge built to SAAMI specifications, but correctly not lock on a "No-go" gauge built to NATO specifications. This is because military weapons are generally designed to operate with wider tolerances and military ammunition cases are generally thicker than commercial ammunition and can tolerate more stretching without rupturing. Therefore, a military firearm may fail the test using SAAMI gauges, but still be deemed somewhat safe to fire per the military specification gauges. However, if it passes even with using SAAMI gauges, that means it is very likely to work correctly.

Go, No-go and Field gauges are available from many firearm supply stores and cost about $25 to $50 per gauge or about $70 to $140 per set.

Saturday, October 12, 2013

It has been a while since the last article. Today, we will study an important concept called "Headspacing". This will be a two-part post.

The term "headspacing" is defined as the distance between the face of the bolt and a point in the chamber that prevents further forward movement of a cartridge.

Click on image to enlarge. Public domain image.

In the above pictures, we have a .45 ACP cartridge loaded into a chamber. The cartridge case is a bit larger than the bullet and the chamber is shaped so that it fits the case correctly. Of course, depending on the shape of the cartridge, the headspacing could be different for different firearms.

For instance, some of the earliest metallic cartridges were rimmed. This means, they have a rim at the base of the cartridge that is larger than the diameter of the cartridge case. When this type of cartridge is pushed into a firearm's chamber, the rim positions the cartridge correctly and prevents it from slipping too far into the chamber. Therefore, for a rimmed cartridge, the proper headspacing should be the width of the rim.

Headspacing of a rimmed cartridge. Click on image to enlarge.

The most popular cartridge today, the .22 Long Rifle rimfire cartridge is an example of a rimmed cartridge.

However, it must be noted that most modern cartridges are rimless (i.e.) the diameter of the rim is the same or smaller than the diameter of the case body. Modern cartridges have other ways to ensure that the bullet seats in the chamber correctly. For example, for most pistol cartridges, the case diameter is slightly larger than the bullet and the chamber has a shoulder that the case mouth rests against.

Headspacing on a .45 ACP rimless cartridge. Click on image to enlarge.

In the image above, we see a .45 ACP rimless cartridge seated in a chamber. The case mouth is larger than the bullet diameter and rests against the front of the chamber, thereby correctly seating the cartridge.

Other rimless cartridges, such as bottle-necked cartridges (which are mostly used by rifles), the shape of the firearm's chamber is correspondingly tapered to achieve proper headspacing.

Headspacing on a bottlenecked rimless cartridge. Click on image to enlarge.

In the above image, we see that the chamber is tapered to accommodate the cartridge and the headspacing is the distance from the bolt face to the tapered section.

In the case of belted cartridges (such as the hunting cartridge, Holland & Holland .300 Magnum), the chamber is shaped to seat the forward face of the belt.

Headspacing on a belted cartridge. Click on image to enlarge.

When the H&H .300 Magnum was first being developed, it was difficult to provide proper headspacing for a cartridge with a shallow shoulder design. The solution was to add a belt around the cartridge body. This is similar in function to the rim of a rimmed cartridge, but gave a long enough surface for the cartridges to fit side-by-side in a magazine, without risk of interference during the feed stroke. This idea was later copied by other magnum rifle cartridges as well.